Well, looking now more carefully at the code, it is in fact correct.
The constants 16807 and 127773 are chosen so that their product is 2147480811, which is smaller enough than 2^31 to prevent overflows in the line:
s = 16807 * (s - k * 127773) - 2836 * k;
where s is known to be positive and less than 2^31, and (s - k * 127773) is the remainder from the division of s by 127773, and k is the quotient of that division.
Adding 2^31 - 1 to a negative 32-bit number cannot produce an overflow in:
if (s < 0) s += 2147483647;
So both the parent comment and my initial confirmation were wrong, the library code is correct. Initially I have replied too quickly, without reading the source. because most such congruential generators are written to use modular arithmetic, while this one has been carefully modified to obtain an equivalent result using integer arithmetic (which also makes it much slower than what can be done with modular arithmetic, so the reason for this is unclear).
The only thing that can be criticized is the lack of a comment emphasizing that those constants cannot be modified haphazardly, otherwise integer overflows are certain.
So your test has verified that the code is correct, so no overflows happened.
Your large seed becomes -1 after conversion to long on a 32-bit system, or it retains its value on a 64-bit system.
For different reasons, in both cases there are no overflows (on a 64-bit system, long is 64-bit, so overflows would have been avoided even with much wider allowable ranges for the constants; the constants are optimized for systems with 32-bit longs, where they are just below the limit for overflows).
Some other values that are either negative or larger than 2^31 may cause overflows, but they are illegal for this function.
Thank you for the explanation. This looks to be correct, e.g. by changing 16807 to 16808 and using the sanitize options, the program can indeed terminate with SIGILL depending on the value of seed.
The constants 16807 and 127773 are chosen so that their product is 2147480811, which is smaller enough than 2^31 to prevent overflows in the line:
s = 16807 * (s - k * 127773) - 2836 * k;
where s is known to be positive and less than 2^31, and (s - k * 127773) is the remainder from the division of s by 127773, and k is the quotient of that division.
Adding 2^31 - 1 to a negative 32-bit number cannot produce an overflow in:
if (s < 0) s += 2147483647;
So both the parent comment and my initial confirmation were wrong, the library code is correct. Initially I have replied too quickly, without reading the source. because most such congruential generators are written to use modular arithmetic, while this one has been carefully modified to obtain an equivalent result using integer arithmetic (which also makes it much slower than what can be done with modular arithmetic, so the reason for this is unclear).
The only thing that can be criticized is the lack of a comment emphasizing that those constants cannot be modified haphazardly, otherwise integer overflows are certain.
So your test has verified that the code is correct, so no overflows happened.
Your large seed becomes -1 after conversion to long on a 32-bit system, or it retains its value on a 64-bit system.
For different reasons, in both cases there are no overflows (on a 64-bit system, long is 64-bit, so overflows would have been avoided even with much wider allowable ranges for the constants; the constants are optimized for systems with 32-bit longs, where they are just below the limit for overflows).
Some other values that are either negative or larger than 2^31 may cause overflows, but they are illegal for this function.